The present invention relates to aqueous solutions of toremifene or a pharmaceutically acceptable salt thereof for pharmaceutical use and to methods for the preparation thereof. The invention also relates to novel salts of toremifene useful in the preparation of water-soluble formulations, in particular aqueous solutions, of toremifene.
Toremifene is a triphenylethylene antiestrogen useful in the treatment of cancer. The preparation of toremifene and its salts is described in U.S. Pat. No. 4,696,949. The salts described are citric and hydrochloride salts. Toremifene is commercially used as a citrate salt. Toremifene base as well as its citrate and hydrochloride salts are poorly soluble in water. Therefore there is a need for stable aqueous formulations of toremifene which would be suitable for e.g. high concentration parenteral, transdermal or topical formulations of toremifene. Parenteral formulations of toremifene in the form of an emulsion, liposome or cyclodextrin complex have been described in WO 93/11757. Transdermal formulations of toremifene in DMSO/ethanol/methylcellulose/water have been described in WO 93/19746. However, these prior formulations are cumbersome to prepare, are irritating or do not provide sufficiently high concentration solutions of toremifene.
It has been found that aqueous solutions of toremifene with high drug concentrations can be prepared by using lactic acid, acetic acid, formic acid, methanesulfonic acid or the corresponding anion (lactate, acetate, formate or mesylate) as a solubility enhancing agent. Furthermore, it was found that toremifene forms stable salts with these anions, and these novel salts are useful in the preparation of water-soluble formulations, in particular aqueous solutions, of toremifene.
The present invention provides an aqueous composition of toremifene or a pharmaceutically acceptable salt thereof comprising lactic acid, acetic acid, formic acid, methanesulfonic acid or the corresponding anion (lactate, acetate, formate or mesylate) as a solubility enhancing agent.
The present invention also provides a method for preparing aqueous composition of toremifene or a pharmaceutically acceptable salt thereof comprising contacting toremifene or a pharmaceutically acceptable salt thereof with aqueous media and a solubility enhancing agent selected from the group consisting of lactic acid, acetic acid, formic acid, methanesulfonic acid or the corresponding anion (lactate, acetate, formate or mesylate).
Furthermore, the present invention provides a novel salt of toremifene with an acid selected from the group consisting of lactic acid, acetic acid, formic acid or methanesulfonic acid. The novel salts are toremifene lactate, toremifene acetate, toremifene formate and toremifene mesylate.
The compositions of the invention can be prepared e.g. by mixing an amount of a solubility enhancing acid of the invention and purified water, adding thereafter toremifene base or a pharmaceutically acceptable salt thereof and agitating the mixture. pH may be adjusted with a water solution of corresponding acid salt or e.g. sodium hydroxide. The solubility enhancing agent is preferably used in molar excess with respect to toremifene or a pharmaceutically acceptable salt thereof. More preferably, the molar excess is at least about 1.5 fold, and most preferably at least about 2 fold, e.g. from about 2 to about 100 fold, typically from about 2 to about 10 fold.
For example, up to about 50 w-% solutions of toremifene base can be prepared by adding a two fold molar excess of lactic acid and purified water. When pH is adjusted to about 5 with sodium hydroxide, still about 36 w-% solutions of toremifene base can be prepared. Generally, when pH is increased, solubility is decreased. The optimum pH range for the solution is about 6 or lower, due to the pKa value (8.0) of toremifene. Various additives used in the art such as preservatives, e.g. parabens, sodium benzoate or benzoic acid, or various combinations thereof may be used.
The salts of toremifene with lactic acid, acetic acid, formic acid or methanesulfonic acid can be prepared by dissolving toremifene base in suitable organic solvent together with an equivalent amount of lactic acid, acetic acid, formic acid or methanesulfonic acid. The mixture is refluxed and cooled. The formed salt is recovered by filtering or by evaporating to dryness. Suitable organic solvents include lower alcohols and ethers, preferably methanol or diethyl ether. The salts can be formulated into any one of a number of known dosage forms or delivery systems by means known in the art e.g. for oral, parenteral, transdermal or topical use. Preferably the salts of the invention are used for preparing aqueous formulations of toremifene. The salts of the invention have generally improved water solubility over toremifene citrate. For example, the solubility of toremifene mesylate in distilled water is about 70 times higher.
The following experiments demonstrate that the water-solubility of toremifene base can be dramatically improved by using a solubility enhancing agent of the invention. The experiments also compare the effect of solubility enhancing agents of the invention to other acids such as hydrochloric acid, gluconic acid or citric acid.